Measurement and analysis of the longitudinal level irregularity of the track beam in monorail tour-transit systems

Notable effects on the vertical dynamic response of vehicle-bridge systems are introduced by longitudinal level irregularity (LLI). However, in monorail systems, the measured data and associated spectrum of the LLI, i.e., the distribution curve of power spectral density versus wavelength, have not been reported in detail. To address this issue, we propose the inclination correction method (ICM) to measure the LLI in monorail tour-transit systems and further estimate and fit the spectral curves for the first time. The measuring principle of ICM is thoroughly described, and ICM is compared with conventional chord-based methods. In addition, the trend components of the measured LLI are eliminated through an adaptive method preceding spectral estimation to avoid potential errors. Notably, a simulation program is designed, and the results from existing methods are adopted to verify the proposed ICM. Based on an analysis of the results, the accuracy and robustness of ICM are demonstrated, and the applicability and advantages of autoregressive models and the proposed fractional functions in spectral analysis are revealed. Finally, combining qualitative and quantitative calculations, an evaluation approach for the generic spectra of monorail LLI is established.